Method and apparatus for forming dye sublimation images in solid plastic

ABSTRACT

Method for forming a dye sublimation image in a substrate, particularly a plastic substrate, and apparatus to perform the method. According to the method taught by the present invention, a substrate is disposed on a perforated platen and a dye carrier having an image formed thereon of a dye sublimation ink is disposed on the substrate such that the image is in contact with the substrate. The substrate, dye carrier and at least a portion of the perforated platen are then covered with a flexible membrane. A clamping pressure is then applied to the substrate and the dye carrier through the membrane. Once the clamping pressure is attained, the substrate and dye carrier are first heated, then cooled.

RELATED APPLICATIONS

This is a Divisional application of co-pending prior U.S. applicationSer. No. 09/823,290 (Atty. Dkt. No. FSCOP001), entitled “METHOD ANDAPPARATUS FOR FORMING DYE SUBLIMATION IMAGES IN SOLID PLASTIC”, filed onMar. 29, 2001, which is incorporated herein by reference and from whichpriority under 35 U.S.C. § 120 is claimed.

FIELD OF THE INVENTION

The present invention relates to the formation of images within solidsheets of plastic. More particularly, the present invention relates to amethodology for forming dye sublimation, or dye transfer, images withinsolid sheets of plastic and to an apparatus for performing themethodology.

BACKGROUND OF THE INVENTION

From the advent of plastics, users and manufacturers thereof have soughta workable means for imprinting or forming images thereon. Prior imagingtechnologies suitable for use on other materials, for instance metals,wood, and the like, have not generally met with success when used toperform permanent imaging on plastics. Examples of such prior imagingtechnologies include but are not limited to paints, decals, lacquers,and dyes. In general the problems associated with utilizing priorimaging or marking technologies center on certain chemical and physicalproperties of plastics in general.

One of the great advantages of plastics is that they can be formed intocomplex shapes having inherently very smooth surfaces. While this is anadvantage in the manufacture of such plastic objects, the extremelysmooth and often chemically resistant nature of plastic surfaces rendersthe application thereto of paints and the like less than satisfactory.Many paints, for instance enamels, when applied to plastics tend toflake or peel when the plastic is flexed or when the image is subjectedto physical distress such as abrasion or temperature change.

In searching for a methodology for forming permanent, abrasion-resistantimages in sheet plastics workers in this field have noted that plasticstend to be molecularly similar to certain fabrics which are imagedutilizing a dyeing process known as “dye sublimation”. According toknown dye sublimation processes, an image, for instance a decorativedesign, is formed of sublimation printing inks on a dye carrier,sometimes also referred to as a transfer paper or auxiliary carrier. Dyecarriers are often, but not exclusively, formed of paper. Printing theimage on the dye carrier is carried out by any of several known printingmethods including, but specifically not limited to offset or rotaryprinting methods. The print images formed on the dye carrier aretransferred by sublimation, also called transfer printing, from the dyecarrier to the textile or fabric which is to be decorated with thedesign.

There are several known dyestuffs suitable for use with dye sublimationprinting techniques. The actual dyestuff or dye carrier utilized is notessential to the principles of the present invention, provided that thedyestuff is capable of sublimation. This is to say that the dyestuffsublimates directly to the vapor state from the solid state upon theapplication of heat. One type of printing ink suitable for sublimationprinting is prepared from sublimable dyestuffs utilizing binders andoxidation additives. The term “sublimable” is defined herein to meancapable of sublimation.

Currently, to form a dye sublimation image in a textile, the printed dyecarrier is placed with its color-imprinted side on the textile face tobe imprinted and is thereafter heated. As soon as the dyestuffs reach atemperature of from about 170 to about 220 degrees Celsius, thosedyestuffs sublime into the textile and the desired image is therebyformed in that textile.

From the foregoing discussion, it will be appreciated that one of theadvantages of dye sublimation printing is that the image is actuallyformed within the structure of the textile, or substrate, on which it isimprinted. This is in direct contrast to most printing techniques,wherein the image is formed solely on the surface of the substrate.While surface-formed images are completely suitable for manyapplications, they are less than optimal for others. By way ofillustration, in the preceding discussion of dye sublimation imagesformed in textiles, it will be appreciated that if a textile issubjected to substantial wear, as is a carpet, an image formed solely onthe surface of that carpet, or on the surface of the individual carpetfibers, will tend to wear quickly.

It will further be appreciated that most inks suitable for formingsurface images tend to be opaque. Again, this is perfectly suitable formany applications. However, where it is desirous that the resultantarticle has a lustrous or translucent property, the use of such opaqueinks precludes the desired translucent image.

U.S. Pat. No. 3,649,332 to Dybvig discloses an early attempt at transferprinting of plastics. According to '332, a photo-sensitive dye carrierhaving an image formed thereon is placed against a porous papertemporary receptor sheet on a vacuum platen and sufficient vacuum isestablished to hold the two sheets in close contact and in fixedposition. The transfer sheet has a dye coating on the surface contactingthe receptor sheet and a photoconductive zinc oxide coating on the outersurface. The outer surface is exposed to a color separation light imagefrom a positive color original, to impart a latent image.

A conductive roller carrying a coating of conductiveradiation-absorptive toner particles at a high potential is passed overthe exposed surface to deposit toner at the non-light-struck areas. Thesurface is then briefly exposed to intense infrared radiation causingtransfer of dye to the receptor at the infrared absorptive toned areas.The vacuum is then released, and the photosensitive sheet is removed andreplaced with a second photo sensitive sheet carrying a second dye, andthe process is repeated utilizing an appropriate color separationfilter. This process is again repeated using a third filter andsensitive sheet to produce a full three-color intermediate.

One or more portions of the intermediate are then cut from the sheet.These segments are placed against a transparent dye-receptive film in adesired arrangement, and over them is placed a paper dye source sheethaving a blue dye coating as previously described, but minus thephotoconductive coating of the transfer sheet. The three layers arepressed together and briefly heated. Thereafter the film is removed andis found to retain a brilliantly clear, full-color copy of the detailsections on an equally clear blue background.

U.S. Pat. Nos. 4,059,471, 4,202,663, and 4,465,728 to Haigh, or Haigh etal. detail methodologies for forming dye transfer images in plasticsurfaces, especially thin films. These several patents flow eitherdirectly from, or as a divisional or continuation in part of, U.S.patent application Ser. No. 540,383 filed Jan. 13, 1975. Each of thesepatents utilize a dye transfer process for forming a dye pattern on adye receptor plastic web, most especially thin films of from 2 to 20mils in thickness, by interposing a carrier web, for instance apolyolefin carrier web, between the dye receptor plastic web and atransfer web containing dispersed dyes. Thereafter the several webs arepressed together in close contact and are heated to a sublimationtemperature suitable for the dyes, and the several webs are maintainedat the sublimation temperature until a substantial portion of the dyeshave sublimed and transferred from the transfer web through thepolyolefin web to the dye receptor web. Thereafter the several webs arecooled below the softening temperature of the dye receptor web, and thedye receptor web is separated from the other webs.

U.S. Pat. No. 4,242,092 to Glover teaches a method of sublimaticprinting on air-permeable sheet structures such as carpets or tiles.According to '092, an air-permeable sheet structure is imprinted byplacing an air-permeable printing foil carrying on one side thereof asublimatic dyestuff in a face-to-face relationship, and in closeproximity, with the air-permeable sheet structure. The side of the foilhaving the dyestuff imprinted thereon is placed in contact with theair-permeable sheet structure, and the foil is heated at a temperatureand for a period of time suitable to vaporize the dyestuff. At the sametime a gas or vapor pressure differential is applied so as to create aflow of air from a space above the foil, and through both the foil andthe sheet structure, thereby causing the dyestuff vapor to flow into thesheet structure and to form an image therein.

U.S. Pat. No. 4,662,966 to Sumi et al. teaches an apparatus for transferprinting a plurality of articles, for instance typewriter keys, whichare held on a plane in rows and then heated. '966 discloses that thisapparatus further includes conveyors for conveying the plurality ofarticles to a heating outlet, the heating outlet having infraredradiation heaters provided inside. The apparatus further includes aholding device for holding the articles at a predetermined position withrespect to the article holder. Another holder is designed to hold atransfer sheet at a second predetermined position. The transfer sheethas a pattern layer formed thereon of thermo-diffusable dye. There isalso provided a means for pressing the transfer sheet against thearticles so that the pattern is transfer-printed on the articles, and aconveyor for conveying the article holder with the plurality of articlesthereon through the heating apparatus and the various holding devices.

U.S. Pat. No. 4,664,672 to Krajec et al. teaches a method for transferprinting onto objects made of plastic, or having a plastic surfacecoating, by pressing a thin dye carrier on the surface to be printedduring the dye transfer process. This is effected by means ofsuper-atmospheric gas pressure, whereby the surface is kept at atemperature below the thermoplastic range of the plastic object.According to the methodology taught by '672 a dye carrier, for instancea paper dye carrier, is pre-dried below the sublimation temperature ofthe ink. The dye carrier is clamped, for instance in a spectacle framein close proximity above but not touching the surface to be printed.Thereafter a gas under pressure is applied to the backside of thecarrier, which gas exerts a slight super-atmospheric pressure directlyor indirectly against the backside of the dye carrier, pressing thecarrier against the object. Thereafter a heat source, for instance aheat radiator, is placed so that its radiation is directed toward thebackside of the dye carrier.

U.S. Pat. No. 5,308,426 to Claveau teaches a process for formingsublimation images on objects, evidently irregular non-planar objects,by forming an “ink support” from a material which is both extensible andair permeable and which will conform to the shape of the object. Thisink support is used to envelop the object, which is then placed in avacuum machine. The vacuum machine, with the ink support inside, is thenintroduced into a heated space, causing transfer of the decoration overthe whole surface of the object be decorated. Examples of extensibleair-permeable materials suitable as ink carriers for utilization in the'426 invention include woven fabrics, knitted fabrics, and sheets ofnon-woven material.

U.S. Pat. No. 5,997,677 to Zaher teaches a methodology for applying acolored decorative designed on a plastic substrate by heating thecarrier and then placing the carrier in contact with the substrate byair suction, such that a sub-pressure results between the carrier andthe substrate. Thereafter an inhomogeneous exposure of infraredradiation is directed to the carrier in correspondence with theprevalent color portion of the dyestuff to which the radiation isapplied. The dye carriers taught by '677 “ . . . above all are sheets ofpaper which, on the one hand, are good at accepting the images ofsublimable dyes to be transferred and, on the other hand, aresufficiently permeable so that air can be sucked through the dye carrier. . . during sublimation transfer printing.” Many of the known dyesublimation printing methodologies applied to solid plastics are sosensitive to variations in pressure, temperature, dye lot, substratelot, and other manufacturing variables, that at least one inventor hasdirected his inventive efforts solely to the task of pre-conditioning aplastic substrate for dye sublimation printing. This pre-conditioning istaught and explained in U.S. Pat. No. 5,580,410 to Johnston.

Given that the formation of precise, vibrant, durable images in solidplastic sheets is a long-sought goal of the plastics imaging industry,why are there currently no flat solid sheets of plastic which have beenimprinted utilizing this methodology, which sheets are formable intocommercial articles? The lack of success on the part of other inventorsin this field is largely due to the fact that while the inventionsdisclosed in the previously discussed patents may theoretically becapable of implementation, in actual practice their use has failed toproduce imaged flat plastic sheets at commercially acceptable costs orin commercially acceptable volumes. There are several reasons for thislack of success.

The first reason that many known processes have not resulted incommercially successful imaged articles is that they are slow. Animaging process which requires an extended period of time tosuccessfully form an image, or which requires a large number of complexand delicate steps to effect, may result in a successfully imaged flatplastic sheet, but one whose imaging is so expensive as to render itcommercially non-viable. Moreover, previous imaging processes are sosensitive to temperature variations that very slight changes inprocessing temperatures result in unacceptable images or destroyedsubstrates.

The second reason that many of these known processes have failed toyield the desired result is closely related to some of these processvariables previously discussed. One particularly aggravating shortcomingof many prior dye sublimation imaging processes is that, in order toform the dye sublimation image in a solid plastic substrate, thatsubstrate must have its temperature elevated above its thermoplasticlimit. In many cases this results in substantial liquefaction of thesubstrate, with attendant unwanted adhesion of the dye carrier to thenow liquefied and sticky substrate. This of course results in asubstrate having at least a portion of the dye carrier adhered thereto,often permanently. Even where it is possible to scrape the adhered dyecarrier from the cooled substrate, this scraping not only results in apoor surface finish, but also requires significant cost in terms ofadditional man-hours to effect.

Some of the previously discussed inventions, in order to obviate theunwanted adhesion of dye carriers to sticky substrates, have relied uponplacing some material between the substrate and the dye carrier.Examples of these materials include parting compounds, such as talcum,or permeable webs. The introduction of such parting or separatingmaterials may preclude, in some instances, the unwanted adhesion of thedye carrier to the substrate, but this is done with significantdegradation of the imaged article. These methodologies are admitted tocause degradation in surface finish, image resolution, or imageregistration on the substrate.

Finally, and most importantly, when applied to solid plastic sheets,known dye sublimation imaging processes tend to shrink, warp and distortthose sheets. While the degree of shrinkage, warping, and distortionvaries from process to process and substrate to substrate, these defectsencountered utilizing known dye sublimation imaging technologies resultin anything from mildly rumpled surfaces to wildly distorted sheetshaving all the planarity of potato chips. Since the object of dyesublimation imaging of solid plastic sheets is to form an image withinthe sheet while retaining its substantially planar nature in anun-shrunken, un-warped and distortion-free state, none of the knownprocesses can be said to be fully successful. Moreover, one or more ofthe technical performance specifications of plastic sheets imaged byother dye sublimation processes are often lost be subjecting the sheetsto the process. These technical performance specifications include, butare not limited to shrinkage, impact resistance, dimensionality, andmechanical strength.

What is clearly needed is a methodology for forming a durable, clear,sharp, image in a solid, flat sheet of plastic by means of a dyesublimation process that results in an un-shrunken, un-warped,distortion-free plastic sheet which retains all of the original plasticsheet's technical performance specifications.

What is further needed is a dye sublimation imaging methodology thatcompletely obviates the unwanted adhesion of the dye carrier to thesubstrate during imaging.

Finally what is needed is at least one apparatus capable of performingsuch a methodology.

SUMMARY OF THE INVENTION

The present invention provides a methodology for forming a dyesublimation image in a solid sheet of plastic. The methodologycompletely obviates the unwanted adhesion of dye carriers to substrates.The imaging methodology taught herein routinely produces a durable,clear, sharp image in a flat plastic sheet, which sheet is un-shrunken,un-warped, and distortion-free and which retains all of its originaltechnical performance specifications.

In order to attain these advantages, the present invention teaches amethod wherein a substrate is disposed on a perforated platen and a dyecarrier having an image formed thereon of a dye sublimation ink isdisposed on the substrate such that the image is in contact with thesubstrate. The substrate, dye carrier, and at least a portion of theperforated platen are then covered with a flexible membrane. A uniformclamping pressure is then applied to the substrate and the dye carrier.One means of attaining this uniform clamping pressure is by inducing apressure differential between the ambient atmosphere and the atmosphereunder the membrane. Once the clamping pressure is attained, thesubstrate and dye carrier are first heated to a temperature sufficientto effect the dye sublimation imaging and retained at that temperaturefor a period of time sufficient to cause the imaging, then they arecooled to a point where the substrate again becomes rigid. The heatingand cooling taught herein effect a first and a second thermal event,both performed while the substrate is under clamping pressure. The firstand second thermal events, in operative combination, not only form theimage and preclude the unwanted warping, twisting, or shrinkage of thesubstrate, but also preclude the unwanted adhesion of the dye carrier tothe substrate.

The invention disclosed herein further teaches a number of novelapparatuses to effect the method, resulting in significantly superiordye sublimation imaging than heretofore attainable.

These and other advantages of the present invention will become apparentupon reading the following detailed descriptions and studying thevarious figures of the Drawing.

BRIEF DESCRIPTION OF THE DRAWING

For more complete understanding of the present invention, reference ismade to the accompanying Drawing in the following Detailed Descriptionof the Invention. In the drawing:

FIGS. 1A-H are cross-sectional views through a platen assembly accordingto the present invention, demonstrating the method thereof.

FIGS. 2A-C are frontal views of a first apparatus for performing themethod of the present invention.

FIG. 3 is a perspective view of the first apparatus for performing themethod of the present invention.

FIGS. 4A-C are frontal views of a second apparatus for performing thepresent invention.

FIGS. 5A-B are frontal views of a third apparatus for performing thepresent invention.

FIG. 6 is a perspective view of the second and third apparatuses forperforming the method of the present invention

FIG. 7 is a cross-section through a thermal head according to oneembodiment of the present invention employing an active cooling device.

FIG. 8 is a cross-section through a thermal head according to anotherembodiment of the present invention employing an alternative activecooling device.

FIG. 9 is a cross-section through a thermal head according to anotherembodiment of the present invention employing both active and passivecooling devices.

FIG. 10 is a cross-section through a thermal head according to oneembodiment of the present invention employing a passive cooling device.

FIGS. 11A-F are cross-sections taken through an alternative platenassembly.

FIG. 12 is an elevation view of a platen rack having loaded therein aplurality of alternative platen assemblies.

FIG. 13 is an elevation view of a platen rack having loaded therein aplurality of alternative platen assemblies, the platen rack beingreceived into an oven.

FIGS. 14A-E illustrate an alternate vacuum bag implementation of thepresent invention.

FIG. 15 is a graph of temperature over time for one dye sublimationimaging cycle, having superimposed thereon a time line indicating theseveral control actions required to effect the cycle.

Reference numbers refer to the same or equivalent parts of the inventionthroughout the several figures of the Drawing.

DETAILED DESCRIPTION OF THE INVENTION

The succeeding discussion centers on one or more preferred embodimentsof the present invention, implemented by a number of components. Thosehaving skill in the art will understand that where the embodimentsenumerated herein specify certain commercially available components,these are by way of example. The principles of the present invention arecapable of implementation in a wide variety of configurations and theseprinciples specifically contemplate all such embodiments.

Having reference now to FIGS. 1A through 1H, a methodology taught by thepresent invention for forming dye sublimation images in substrates,particularly in solid plastic substrates, is shown. At FIG. 1A is showna platen, 10, having superimposed thereon a passive cooling device, 12.The principles of the present invention specifically contemplate theutilization of either or both active and passive cooling devices, aswill be explained later. Platen 10, in one embodiment of the presentinvention, is a flat aluminum plate transfixed by a plurality of vacuumorifices 14. Vacuum orifices 14 are further connected to a vacuumsystem, 240. Placed atop passive cooling device 12 for purposes offorming a dye sublimation image therein is substrate, 1. In order toform the dye sublimation image, dye carrier 3 having an image, 5,imprinted thereon utilizing the previously discussed dye sublimationinks, is placed atop substrate 1.

While the succeeding discussion is directed to the dye sublimationimaging of plastic sheets and the like, the principles of the presentinvention,may advantageously be applied to the dye sublimation imagingof a wide variety of man-made and naturally occurring sheet materialsubstrates, including but specifically not limited to metals, stone,wood, waxes, polymers, monomers, resins, textiles, fabrics, glasses,minerals, and composites thereof. The principles of the presentinvention specifically contemplate all such applications.

The passive cooling device 12 of this embodiment of the presentinvention consists of a panel having an extremely low thermal mass, forreasons which will be later explained. One embodiment of the presentinvention contemplates the utilization of a hex-cell aluminum-coredcomposite sandwich panel having glass-reinforced plastic upper and lowersurfaces. One such panel suitable for implementation as passive coolingdevice 12 is a Fiber-Lok No. 2330 sandwich panel available from BurnhamComposites, Wichita Kans. According to this embodiment of the presentinvention, passive cooling device 12 is of smaller surface extent thanplaten 10, but is at least as broad in extent as the substrates whichwill be processed on it. This is necessary in order that there be atleast some of the plurality of vacuum orifices 14 available to form avacuum path for membrane 16, as will be subsequently explained.

Referring now to FIG. 1B, membrane 16 is applied over the stackcomprising cooling device 12, substrate 1, and dye carrier 3. Membrane16 further overlaps at least a portion of platen 10. Membrane 16, forease of handling, may be fitted to a spectacle frame, not shown in thisfigure. Membrane 16 should be capable of forming a substantiallyairtight seal for purposes of clamping the substrate-dye carrier stacktogether in close proximity. Membrane 16 should also have sufficientstrength to prevent the warping of substrate 1 during the thermal eventswhich constitute one dye sublimation cycle and which enable dyesublimation imaging and dye carrier removal, as will be later explained.

Other properties desirable of membrane 16 are that it is substantiallychemically compatible not only with substrate 1 and the sublimatic dyesimprinted on dye carrier 3, but also with any byproducts out-gassed fromsubstrate 1 or dye carrier 3 during dye sublimation imaging.

In one embodiment of the present invention, the lower surface ofmembrane 16 is lightly textured to provide a continuous vacuum channelacross the interface between membrane 16 and dye carrier 3 withoutforming bubbles between the membrane and dye carrier. These bubbleswould preclude even clamping of dye carrier 3 to substrate 1. Thistexture also serves as a vacuum release and as a bleeder to trail offthe vacuum when it is no longer needed for clamping.

Moreover, in order to smoothly mold and flow over the several elementsof the cooling device-substrate-dye carrier stack, as well as to platen10, it is desirable that membrane 16 be formed of a flexible material.When used on dye carrier-substrate-cooling device stacks havingsignificant vertical extent, for instance greater than about one inch inthickness, it further desirable that the membrane be formed of anelastomeric material to more smoothly mold and flow over these severalelements. As the imaging process taught herein utilizes rapidtemperature changes, as well as sustained periods of temperatures up to600° F., is also required of the membrane that it be not onlyheat-resistant, but that it be capable of withstanding repeated thermalcycles between higher and lower temperatures without hardening,cracking, loss of structural integrity or loss of any of the previouslydiscussed properties.

From the foregoing discussion it will be appreciated that a number ofmaterials are suitable for membrane 16. Examples of such materialsinclude, but are specifically not limited to: vulcanized rubbers,silicones, butyl rubbers, polymers, chloropolymers, fluoropolymers, andother natural or man-made elastomeric sheets. Membrane 16 is broughtinto substantially continuous contact with dye carrier 3, and coverssubstantially all of the plurality of vacuum orifices 14 not previouslycovered by passive cooling device 12.

Referring now to FIG. 1C, the clamping step of one embodiment of thepresent invention is explained. Membrane 16 having previously beenpositioned over the dye carrier-substrate-cooling device stack, as wellas at least a portion of platen 10 including at least one and preferablya plurality of vacuum orifices 14, now exerts an atmospheric clampingpressure, as shown at 20. As used herein, the term “atmospheric clampingpressure” denotes the use of a pressure differential between the ambientatmosphere and the atmosphere beneath the membrane to effect theclamping of the substrate and dye carrier. This atmospheric clampingpressure may be effected by means of vacuum, air pressure, or acombination of the two.

In the embodiment under discussion, atmospheric clamping pressure 20 isattained by means of connecting at least one of a plurality vacuumorifices 14 to a vacuum system, 240, and thereby applying a vacuum, asshown at 18, to the underside of membrane 16. It should be noted thatvacuum system 240 has been deleted from FIGS. 1A-B and D-H for purposesof illustrational clarity. Where a substantially perfect vacuum isobtainable at sea level, this theoretically results in a clamping forceof approximately 14.7 psi over the entire surface of the dyecarrier-substrate stack. Practically, a perfect vacuum is seldomobtainable and in any event is not generally necessary. Clamping forcesequating to 14 psi resulting from less than perfect vacuum have beenfound to yield dye transfer images vastly superior to those obtainableby any other methodology. Depending upon the mechanical properties ofthe substrate, the dye transfer temperatures, and the nature of thethermal events occasioned by the application of the principles of thepresent invention, even lower clamping pressures may be utilized.

While the foregoing embodiment utilizes vacuum clamping, alternativeembodiments utilize other means of attaining the very even clampingpressure afforded by vacuum clamping. These alternatives include, butare not necessarily limited to the use of mechanical clamping padsincorporating a pressure-leveling layer, for instance foam rubber orsacrificial rigid foam sheets, and the use of air pressure clamps, forinstance bag presses.

It should also be noted that clamping pressure, including the previouslydiscussed vacuum clamping pressure, may serve as a processing controlvariable. For some imaging routines in some substrates, it may beadvantageous to modify the clamping pressure above or below the nominal1 atmosphere clamping pressure discussed above. Clamping pressures lowerthan 1 atmosphere may be attained and maintained by utilizing a vacuumregulator. Clamping pressures greater than 1 atmosphere may by attainedby augmenting the vacuum clamping pressure with a supplementary clampingforce. One methodology for attaining this latter option is by means of abag press superposed over the membrane, the inflated force of which bagpress supplements the vacuum clamping attained by the membrane alone.

Referring now to figure ID, a first, or heating thermal event forforming a dye sublimation image is imposed on the membrane-dyecarrier-substrate stack as follows: thermal energy is applied throughmembrane 16 and dye carrier 3 to substrate 1. In this embodiment of thepresent invention it has been found advantageous not only in terms ofmanufacturing efficiency, but of efficacy of later removing dye carrier3 from substrate 1, that thermal energy 22 be provided as rapidly aspossible to substrate 1. Thermal energy 22 may be applied throughmembrane 16 in substantially any manner known to those having ordinaryskill in the art that will not damage membrane 16. The previouslyapplied atmospheric clamping force is maintained throughout this step.

Examples of applicable heat transfer methodologies include, but arespecifically not limited to: electrical resistance heating, for instanceby means of electrical resistance wires embedded in membrane 16, orapplied either above or below membrane 16; by the application of steamto an upper surface of membrane 16; by the application to an uppersurface of membrane 16 of a flow of heated gas including steam, flame orheated fluid; or by the application of radiant energy to the top ofmembrane 16. Examples of such radiant energy include but are not limitedto infrared energy applied by means of infrared lamps, or ultravioletradiation, and microwave radiation. Another alternative for applyingthermal energy 22 is the application to an upper surface of membrane 16of a conductive heating source, for instance a heated plate. Again, thisplate may be heated by any known heating methodologies, such as thosepreviously discussed, as well as by introducing into a hollow interiorof the plate a flow of heated fluid or gas.

Plastics, for instance thermoforming plastics, have specificallydifferent physical attributes depending upon their internal temperature.At room temperature most commercially usable thermoforming plastics aresubstantially rigid, for instance as rigid sheets. At the other end ofthe temperature spectrum, heating a thermoforming plastic substantiallyabove its thermoplastic temperature results in the substantialliquefaction of the plastic, with attendant destruction of the structureformed by the plastic as the plastic liquefies. Intermediate betweenthese two extremes are temperatures at which the plastic begins tosoften but is not yet fully liquid. It is at these intermediatetemperatures that the dye sublimation process of the present inventionis conducted.

In order to simultaneously render substrate 1 mechanically andchemically suitable for the introduction of dye, as well as to providefor the sublimation of imaging dyes from the solid to the vapor state,the temperature of the substrate, and hence the dye carrier, must beelevated beyond the plastic's rigid and generally impervious state to astate where the plastic begins to soften, and where the sublimationdyestuffs vaporize. In order to retain the structural integrity of theplastic, and to maintain the technical performance specifications of theplastic, it is necessary that it not be heated to the point where itliquefies. The ideal temperature is of course application specific anddepends not only upon the type and thickness of plastic sheet to beimaged but also upon the nature of the imaging dyes.

The application of thermal energy 22 to raise the internal temperatureof substrate 1 and dye carrier 3 comprises the first thermal event ofthe present invention. The duration of the first thermal event is againapplication specific and is determined empirically. One of the metricsfor determining the duration of the first thermal event is the desireddegree of penetration of the image into the plastic.

Referring now to FIG. 1E, following the first thermal event, whichactually effects the dye sublimation imaging of the substrate 1, asecond, or cooling thermal event is accomplished while the substrate anddye carrier remain under vacuum clamping pressure. Again, the previouslyapplied vacuum, 18, is maintained during this second thermal event thatcomprises the removal of thermal energy at 24. It has been found that asecond, rapid cooling thermal event conducted under vacuum clampingpressure presents advantages over previous dye sublimation imagingtechnologies.

A first advantage accruing from this step is that the release of dyecarrier 3 from substrate 1 is greatly improved over that of previousmethodologies. Indeed, by carefully adjusting the temperature andduration of the first thermal event, in conjunction with the rapidcooling of the second thermal event, the unwanted adhesion of dyecarrier 3 to substrate 1 has been completely obviated. While not wishingto be bound by theory, it is believed that the rapid cooling occasionedby the second thermal event introduces some thermal or mechanical shockbetween dye carrier 3 and substrate 1 which renders these two elementsseparable. This is accomplished without the need for specialintermediate dye transfer webs or time-consuming pre-imagingconditioning processes required by other methodologies.

A second advantage afforded by this step relates to the previouslydiscussed problems of unwanted distortion of the substrate caused by theheating and cooling thereof without benefit of a strong, evenly appliedclamping force over the entire surface of the substrate. Again notwishing to be bound by theory, it is believed that prior dye sublimationtechnologies, by inducing the heating and cooling of the substrate,liberate internal forces within an unconstrained substrate which, oncooling, tend to twist, shrink, and warp the substrate. By utilizing anatmospheric clamping methodology including a tough, yet resilientmembrane 16, for instance the vacuum clamping technology previouslydiscussed, the present invention avoids this problem by forcing theretention of the substantially flat shape of the sheet throughout theseveral thermal events of the dye sublimation imaging process.

Referring now to FIGS. 1F-1H, at the completion of the second, coolingthermal event, vacuum is released at 26 and membrane 16 removed from thedye carrier—substrate stack at 28. Thereafter, dye carrier 3 andsubstrate 1 are lifted from passive cooling device 12. At this point theimage carried by dye carrier 3 has been formed within substrate 1. Thedegree of dye penetration within the plastic is dependent upon severalfactors. These include sublimation temperature, clamping pressure, andduration of application of thermal energy and clamping pressure.

A first apparatus for performing a methodology according to the presentinvention is disclosed having reference to FIGS. 2A-2C and 3. Dyetransfer apparatus 200 includes a table assembly 202, at least oneplaten assembly 204, a thermal imaging unit 206, and a vacuum system240. Table assembly 202 supports thermal imaging unit 206 and platenassembly 204. As will be discussed later, the utilization of a pluralityof platen assemblies 204 presents advantages with respect tomanufacturing efficiency. Accordingly, in one preferred embodiment ofthis apparatus there are provided a pair of platen assemblies 204 and204′, which are substantially identical. Table assembly 202 ispreferably equipped so that platen assemblies 204 and 204′ may beintroduced into thermal imaging unit 206 in rotation. In order to effectthis insertion of platen assemblies 204 and 204′, a system of rollers orslides may be implemented. These rollers are preferably formed as aseries of rollers 220 on table assembly 202, across which platenassembly 204 and 204′ slide. Alternatively, rollers or slides may beprovided on the underside of platen assemblies 204 and 204′. Othersliding-friction reducing methods including air cushions, polished metalslides, and PTFE slides may, of course, be implemented.

Apparatus 200 is further equipped with a vacuum system 240. Vacuumsystem 240 includes a vacuum source, for instance a vacuum pump 242 andoptionally a vacuum reservoir 244, which is connected by piping 245 tovacuum pump 242. This vacuum source is then connected by means offlexible piping 246 and vacuum valve 248 to platen assembly 204, andmore particularly, to vacuum orifices 14 thereof. A similar set ofpiping and vacuum valves, 246′ and 248′ connects the vacuum source toplaten assembly 204′. The actuation of vacuum valves 248 and 248′ may bemanual, remote, or automated. In a preferred embodiment of thisapparatus, vacuum valves 248 and 248′ are electrically controlled valvesoperated from a control station 300.

Referring now to FIG. 2B, details of thermal imaging unit 206 and platenassembly 204 are shown. Platen assembly 204 comprises a perforatedaluminum platen 10, atop which is placed a passive cooling device 12. Aframe, sometimes referred to herein as a “spectacle frame”, 216 ishingedly attached at one side to platen 10 by means of hinges 208. Frame216 has mounted thereto a sheet of elastomeric membrane 16, previouslydiscussed, which membrane covers the aperture formed by the frame. Inthis embodiment of the present invention membrane 16 takes the form ofthe textured sheet of DuPont Viton™.

Thermal imaging unit 206 in this embodiment is a substantially hollowbox-like chassis 207 having mounted therein a heat source. This heatsource may implement substantially any of the previously discussedheating methodologies, and in this embodiment of the present inventioncomprises at least one, and preferably a plurality of electricalinfrared bulbs 208. Chassis 207 is hingedly attached to table assembly202 by means of hinges 210 a suitable distance above the surface oftable assembly 202 such that, when closed, thermal imaging unit 206 ispositionable flushly atop platen assembly 204 when chassis 207 islowered onto platen assembly 204.

The operation of apparatus 200 is further described having reference toFIGS. 2B-C. At the start of one imaging cycle, frame 216 is opened asshown at the left side of FIG. 2B, and a sheet of plastic substrate 1 isinserted atop cooling device 12. Thereafter, a dye carrier 3 having adye image, 5, imprinted thereon is positioned such that dye image 5 isin direct contact with substrate 1. Dye image 5 may be advantageouslyformed by imprinting the image, utilizing substantially any known dyesublimation dyestuff, onto one surface of dye carrier 3. Thereafter,frame 216 is closed over the dye carrier-substrate-cooling device stacksubstantially as shown at the right side of FIG. 2B. Thereafter, vacuumvalve 248 is opened, causing vacuum system 240 to evacuate the areaunder membrane 16. This evacuation seals membrane 16 to platen 10 andthe previously discussed stack, and provides an atmospheric clampingforce to effect the dye transfer process. It also acts to maintain theregistration of the dye carrier 3 with respect to substrate 1, and innovel fashion to preclude the unwanted distortion of substrate 1, aspreviously discussed.

Once suitable vacuum clamping force has been obtained, platen assembly204 is slidably positioned beneath chassis 207 of thermal imaging unit206, and chassis 207 is positioned on top of platen assembly 204. Itshould be noted that the hinged elevation and lowering of both chassis207 of thermal imaging unit 206, and frame 216 of platen assembly 204,may be manually performed, or advantageously may be performed by anylifting methodology known to those having skill in the art. Theselifting methodologies include, but are specifically not limited to,pneumatic cylinders, hydraulic cylinders, servo motors, spring devices,counter weights, screw or geared devices and all other elevating anddepression methodologies known to those having ordinary skill in theart.

After chassis 207 is lowered onto platen assembly 204, infrared bulbs208 are energized causing the heating 22 of membrane 16, dye carrier 3and substrate 1, while dye carrier 3 and substrate 1 remain under thepreviously discussed clamping vacuum. The temperature beneath membrane16 may be monitored by means of a thermocouple 212 positioned betweenpassive cooling device 12 and membrane 16. Alternative temperaturemonitoring methodologies known to those of ordinary skill in the artmay, of course, be implemented. Infrared bulbs 208 remain energized fora specified time empirically determined to be optimal for the substrate,sublimation dyestuff, and degree of dye transfer imaging desired.

Once the specified thermal imaging time has elapsed, infrared bulbs 208may be de-energized, chassis 207 is elevated, and platen assembly 204 isremoved from under chassis 207 while a vacuum is retained under membrane16. The advantages of an embodiment of this apparatus having two platenassemblies 204 and 204′ are now shown. While platen assembly 204 iscooled under vacuum clamping at 24, platen assembly 204′, having beenpreviously loaded and vacuum clamped, is positioned under chassis 207 ofthermal imaging unit 206. Chassis 207 is then lowered onto frame 216 ofplaten assembly 204′ and the heat source, for instance infrared bulbs208, may again be energized. Accordingly, one of platen assemblies 204and 204′ is cooling while the other is heating, while both retain theirrespective substrate/dye carrier stacks under clamping pressure.

In this embodiment of the present invention, which implements a passivecooling device, cooling 24 is accomplished by exposing platen assembly204 to ambient air temperature. This exposure may be augmented byintroducing a flow of ambient air across the surface of platen assembly204, and most especially across membrane 16 by means of a fan or otherairflow-inducing device. Passive cooling device 12 serves to passivelycool substrate 1, dye carrier 3 and at least a portion of membrane 16 inthe following manner: being of very low thermal mass, passive coolingdevice retains little unwanted heat. Once the first thermal event iscomplete, and the second thermal event commenced, passive cooling device12 contributing little additional head, enables the rapid cooling of themembrane and the elements under it.

Again, the temperature beneath membrane 16 is monitored by means ofthermocouple 212 until substrate 1 has reached a temperaturesufficiently cool to return it to its rigid state without distortion.Thereafter, vacuum valve 248 is actuated to relieve the vacuum beneathmembrane 16, thereby releasing the clamping pressure to substrate 1 anddye carrier 3. Once clamping pressure is released, substrate 1 and dyecarrier 3 may be removed from platen assembly 204 after lifting frame216 therefrom. By using two platen assemblies, for instance 204 and204′, to alternatively heat and cool the substrate in this manner,imaging throughput is nearly doubled.

In one application of this embodiment of the present invention an 80 milacrylic sheet was utilized as substrate 1. The acrylic sheet was imagedby positioning it on passive cooling device 12, and then superposing adye carrier 3 thereover, as shown. Spectacle frame 216 was then loweredover the acrylic sheet and dye carrier 3, covering them with membrane16. In this embodiment, a silicone rubber sheet was implemented asmembrane 16. After evacuation of the space under membrane 16, processingproceeds in previously discussed for this embodiment. In this case theacrylic sheet was processed for 10 minutes at a temperature 350° F.After this first thermal event, cooling proceeded as previouslydiscussed.

Where one embodiment of the present invention utilizes radiant heating,as previously discussed, another embodiment utilizes conductive heating.An example of such a conductive apparatus is shown having reference toFIGS. 4A-4C and 6. This embodiment shares many characteristics of thepreviously discussed apparatus, but with one significant difference:where the previously discussed apparatus used radiant heating, thisembodiment utilizes a conductive heating plate, 402. Table 202 andvacuum system 240 are as before, as are platen assemblies 204 and 204′.In this embodiment however, thermal imaging unit 400 defines a lateraltunnel, 450, therethrough.

Conductive heating plate 402 is retractably mounted within a portion ofthermal imaging unit 400 overlying tunnel 450. Conductive heating plate402 in this embodiment is typically retracted upwardly by means of aretractor, in this embodiment one or more tension springs 406.Alternative retraction devices known to those having ordinary skill inthe art, including but not limited to counterweights, pneumaticcylinders, vacuum cylinders, chains, bag presses, cables, hydrauliccylinders, and electromechanical devices may, with equal facility, beimplemented.

Positioned between an upper surface, 403, of conductive heating plate402 and an inner surface 401 of thermal imaging unit 400 is a clampingor urging device, which works in opposition to tension springs 406 tourge conductive heating plate 402 into contact with membrane 16. In theembodiment here illustrated, this urging device takes the form of a bagpress, 404. Bag press 404 is connected to a controllable source ofpressurized gas, or air by means of piping and valves, not shown in thisfigure, to effect the urging of heating plate 402 into contact withmembrane 16. Of course, alternative clamping or urging devices known tothose of ordinary skill in the art may also be implemented to fulfillthis function. Non-limiting examples of such include hydrauliccylinders, pneumatic cylinders, magnetic urging devices to includeelectromagnetic urging devices, camshafts, crankshafts, wedges, andother methodologies for imparting substantially linear motion known tothose of ordinary skill in the art.

Referring now to FIGS. 4B-4C and 10, which depict a cut-away sectionthrough thermal imaging unit 400, the operation of this embodiment isexplained. At FIG. 4A, platen assembly 204 has just been removed fromthermal imaging unit 400. Platen assembly 204′ has been loaded withsubstrate 1 and dye carrier 3, as before. At this point both platenassemblies 204 and 204′ are retained under vacuum clamping pressure bymeans of vacuum valves 248 and 248′ being opened to vacuum system 240.It will be appreciated that conductive heating plate 402 has beenretracted upwardly by means of tension springs 406, rendering platenassembly 204′ slidably insertable into thermal imaging unit 400 by meansof tunnel 450.

Conductive heating plate 402 may be heated by any means known to thosehaving ordinary skill in the art including, but not limited to:electrical resistance wiring; the introduction of heated gases or fluidsinto a hollow interior portion 403 of conductive heating plate 402;radiant or convective heating of the conductive heating plate; openflame including one or more gas jets, as well as substantially any othermethodology of controllably heating a conductive metal plate. In theembodiment depicted in the referenced figures, conductive heating plate402 takes the form of a flat aluminum plate rendered partially hollow bythe formation therein of at least one labyrinthine passage. In theembodiment depicted in this figure, conductive heating plate 402 isconnected by means of piping and valves to an oil heater including anoil circulation pump. The oil heater thus provides a controllable flowof heated oil through the interior labyrinth of conductive heating plate402 when it is desired to heat the plate. The flow of heated oil may bethermostatically controlled by hot oil valve 564 and hot oil piping 562to retain conductive heating plate 402 at a desired temperature, orwithin a desired temperature range.

At FIG. 4C, platen assembly 204′ has been slidably inserted throughtunnel 450 into thermal imaging unit 400, and conductive heating plate402 urged into close contact with an upper surface of membrane 16′ bymeans of bag press 404. This urging is accomplished by introducing acontrolled flow of compressed gas, or air, into an interior portion ofbag press 404 by means of compressed air valve 450 and compressed airpiping 452. Conductive heating plate 402, being heated to a temperaturesufficient to induce the desired sublimation temperature in substrate 1and dye carrier 3, effects that heating of the substrate throughmembrane 16 for the desired period of time. While this first thermalevent is conducted in this fashion, platen assembly 204, havingpreviously been removed from thermal imaging unit 400 is cooled aspreviously discussed, at 24.

Bag press 404 may also be used to increase the clamping pressuredelivered to dye carrier 3 and substrate 1 above the nominal oneatmosphere clamping pressure attainable by means of vacuum clampingalone. In one embodiment of the present invention, it is contemplatedthat the auxiliary clamping force attained by pressurizing the bag pressmay contribute as much as an additional 20 atmospheres of clampingpressure, where the substrate/sublimation dye combination warrants suchelevated clamping pressures.

Once the temperature of substrate 1 has been elevated to the desireddegree for the desired period of time, pressure within bag press 404 isrelieved, again by means of compressed air valve 450 and compressed airpiping 452. Conductive heating plate 402 is then retracted to theposition shown at FIG. 4B by means of tension springs 406. Thereafterplaten assembly 204′ is removed from thermal imaging unit 400 to theposition shown at FIG. 4A, and platen assembly 204, having beenre-loaded following the cooling of its previously imprinted substrate,is ready for insertion into thermal imaging unit 400.

In one application of this embodiment of the present invention an 80 milSintra® sheet was utilized as substrate 1. The Sintra® sheet was imagedby positioning it on passive cooling device 12, and then superposing adye carrier 3 thereover, as shown. Spectacle frame 216 is then loweredover the Sintra® sheet and dye carrier 3, covering them with membrane16. In this embodiment, a Viton® fluoroelastomer sheet was implementedas membrane 16. After evacuation of the space under membrane 16,processing proceeds as previously discussed for this embodiment. In thiscase the Sintra® sheet was processed for 5-7 minutes at a temperature of285° F. Following this first thermal event, cooling proceeded aspreviously discussed.

While the embodiments of the present invention previously disclosedutilize a system of rollers, for instance 220, in order to render platenassemblies 204 slidably positionable under the thermal imaging head, theprinciples of the present invention contemplate alternativemethodologies for positioning platen assemblies 204 and 204′ underthermal imaging unit 400. These methods include but are not limited toforcing one or more platen assemblies 204 vertically into position withrespect to thermal imaging unit 400, and rotatably positioning suchplaten assemblies 204 below thermal imaging unit 400. Moreover, whileplaten assemblies 204 may be manually slid into position with respect tothermal imaging unit 400, the principles of the present inventionfurther contemplate the use of a positioning member, not shown, toeffect the slidable positioning of platen assembly 204. Examples of suchpositioning members include, but are again not limited to, pneumaticcylinders, hydraulic cylinders, gears, screw drives, gear drives,cables, chains, electrical coils, electromechanical devices, and otherpositioning methodologies well-known to those having ordinary skill inthe art.

Referring now to FIGS. 5A-5B, 6, and 7, a further embodiment of thepresent invention implementing an active cooling system is disclosed.Again, table 202, thermal imaging unit 400, and vacuum system 240 aresubstantially as previously disclosed. This embodiment howeverintroduces an active cooling element 550 in place of the previouslydiscussed passive cooling device 12. According to one embodiment of thepresent invention, active cooling element 550 comprises a thermallyconductive flat plate, for instance an aluminum plate, defining thereinat least one internal cavity 551, which is connected to a cooling system520. Cooling system 520 comprises piping 524 and valves 526 connectingactive coolant element 550 to a cooling source 522.

Cooling source 522 may employ substantially any cooling or refrigerationmethodology known to those having ordinary skill in the art. By way ofillustration, but not limitation, such refrigeration methodologiesinclude, but are not limited to the flow of refrigerated liquids andgases, the introduction into cavity 551 of a flow of super-cooledliquid, for instance liquid nitrogen, and the induction by means of asmall orifice from cavity 551 of an expanding flow of gas, resulting inthe cooling of element 551.

The implementation of the methodology taught herein is conductedutilizing this embodiment as follows: once platen assembly 204 has beenintroduced into thermal imaging unit 500 and aligned with respect toconductive heating element 502, a flow of compressed gas, for instanceair, is introduced through valve 452 and pressure piping 450 into theinterior of bag press 404, inflating bag press 404 and urging conductiveheating element 502 downward into intimate contact with membrane 16.Conductive heating element 502 is retained in intimate contact withmembrane 16 by maintaining pressure within bag press 404. This pressuremay be maintained or regulated by means of a pressure regulator, notshown.

Conductive heating element 502 is heated, in this embodiment, by meansof a controlled flow of heated oil from oil heater 560 introduced intoan interior portion 503 of conductive heating element 502 throughheating oil piping 562. The flow of heated oil is controlled by means ofhot oil valve 564. An oil return line, not shown, returns cooled oilfrom conductive heating element 502 to oil heater 560. Thermocouple 212measures the temperature under membrane 16.

Once the temperature under membrane 16 has reached the desiredsublimation temperature, it is maintained at that temperature by meansof a continuing flow of heated oil for the duration of the first, orheating, thermal event. Thereafter, pressure is released from bag press404 by means of valve 452, and tension springs 406 retract conductiveheating element 502 upwardly, compressing bag press 404. A controlledflow of chilled water is then introduced into an interior cavity 551 ofactive cooling plate 550 by means of chilled water piping 524 andchilled water valve 526 from cooling source 522 to effect the second, orrapid cooling, thermal event. A water return line, not shown, returnswarmed water to cooling source 522 for re-cooling. Again, thetemperature of substrate 1 is measured by thermocouple 212, and whensubstrate 1 has been returned to its substantially rigid state, the flowof chilled water into active cooling plate 550 is secured by means ofchilled water valve 526. This concludes the second, or cooling, thermalevent.

At this point platen assembly 204 is slidably retracted from thermalimaging unit 500 through tunnel 450 and the vacuum, which has beenmaintaining clamping pressure on substrate 1 and dye carrier 3, isreleased by means of vacuum valve 248 and vacuum piping 246. Thereafterframe 216 is lifted from platen 10 and both dye carrier 3 and substrate1, now bearing the desired image, are removed from atop active coolingplate 550. Thereafter platen assembly 204′ may be introduced intothermal imaging unit 500 and processing repeated as described above.Platen assembly 204 may be advantageous re-loaded with another blanksubstrate 1 and dye carrier 3, and platen assembly 204 may then bereadied for insertion into thermal imaging unit 500 following thepreviously discussed vacuum clamping process.

Yet another alternative is presented having reference to FIG. 8. Thisembodiment is similar to the embodiment depicted in FIG. 7, but withthis difference: active cooling plate 550 is not utilized in the presentenvironment, but both heating and active cooling are performed by meansof a thermal plate 802. Thermal plate 802 is similar to conductiveheating plate 502 shown in FIG. 7 with the exception that it providesboth heating and active cooling to substrate 1 and dye carrier 3 throughmembrane 16. This is accomplished in the following manner: to effect theheating of thermal plate 802 there is introduced into an internal cavity803 thereof a controlled flow of heated fluid, for instance a 50 percentmixture of ethylene glycol and water, this mixture sometimes hereafterreferred to as “water”, by means of hot water piping 804 controlled byhot water valve 806.

This heated fluid may be heated in a furnace, boiler, or other fluidheating means known to those having ordinary skill in the art. Moreover,in order to attain substantially elevated temperatures without boilingthis heated fluid, the principles of the present invention contemplateraising the pressure within the heating system to prevent the heatedfluid from boiling. Processing proceeds as previously described untilthe desired duration of the first thermal event has been reached. Atthis point, the flow of hot water through hot water piping 804 issecured at hot water valve 806. Thereafter a flow of coolant, forinstance chilled water, which in this embodiment will be understood toinclude the previously discussed mixture of water and ethylene glycol,is then introduced into the internal cavity, 803 of thermal plate 802 bymeans of chilled water piping 524 controlled by chilled water valve 526.This has the effect of rapidly cooling thermal plate 802 andtransforming that unit into a cooling plate. Once again, cooling isapplied to substrate 1 and dye carrier 3, now by chilled thermal plate802, until such time as substrate 1 has been returned to itssubstantially rigid state. Thereafter, processing proceeds as previouslydescribed.

In one application of this embodiment of the present invention a 60 milKydex® sheet was utilized as substrate 1. The Kydex® sheet was imaged bypositioning it on platen 10, and then superposing a dye carrier 3thereover, as shown. Spectacle frame 216 is then lowered over the Kydex®sheet and dye carrier 3, covering them with membrane 16. In thisembodiment, a butyl rubber-covered canvas sheet was implemented asmembrane 16. After evacuation of the space under membrane 16, processingproceeds in previously discussed for this embodiment. In this case theKydex® sheet was processed for 5 to 10 minutes at temperatures from 370°F. to 335° F. Following the first thermal event, a flow of chilled fluidwas introduced into the interior, 803 of thermal plate 802 to cool theKydex® sheet, substantially to room temperature.

An alternative to this embodiment contemplates the utilization ofseparate heating and cooling plates, either in the same thermal imagingunit, or in separate heating and cooling units. These units could besubstantially identical, with the sole difference being the type ofplate, either heating or cooling, employed therein.

Still another embodiment is shown having reference to FIG. 9. Theapparatus shown in FIG. 9 is substantially identical with that describedabove and shown in FIG. 8, with the addition of passive cooling device12. Accordingly, it will be appreciated that this embodiment employsboth active and passive cooling. The utilization of a passive coolingdevice 12 in addition to thermal plate 802 has the advantage that anyunwanted heat transferred by the first thermal event into platen 10 isminimized by the utilization of passive cooling device 12.

Another embodiment of the present invention is disclosed havingreference to FIGS. 11A-F, 12, and 13. This embodiment utilizes a platenassembly 1000 similar to at least one of the previously described platenassemblies. Platen assembly 1000 is however designed to accommodate aplurality of substrate-dye sheet pairs arranged as a substrate stack,1003. At FIG. 11A a substrate, 1 and dye carrier, 3 having image 5imprinted thereon utilizing dye sublimation inks as previouslydisclosed, is loaded as before. Thereafter alternating layers ofsubstrate 1 and dye carrier 3 are loaded until a substrate stack 1003having the desired thickness is formed, a shown at FIG. 11B.

In this embodiment platen assembly 1000 comprises a platen 1001substantially as previously discussed, but further incorporating someclamping device for holding frame 1010 to platen 1001, as shown at FIG.11C. Frame 1010 is substantially like the previously disclosed frames,but has provisions for being clamped to platen 1001. In the embodimentpresented in FIGS. 11A-F, 12 and 13, this clamping is effected by meansof a plurality of bolts 1020 inserted through holes formed about theperiphery of frame 1010 and thereafter inserted through a correspondingplurality of matching holes formed about the periphery of platen 1001.Thereafter a nut 1022 is threaded onto each of bolts 1020 to secureframe 1010 to platen 1001 and capturing, under membrane 16, substratestack 1003. While the clamping together of frame 1010 and platen 1001 inthis example has been effected by the simple expedient of utilizing aplurality of threaded nuts and bolts, study of the principles enumeratedherein will elucidate to those having ordinary skill in the art that awide variety of known clamping methodologies may, with equal facilitymay be implemented. These clamping methodologies include, but arespecifically not limited to, patent clamps, over-center clamps, wedges,C-clamps and other threaded clamps, ratchet clamps, catches, magneticcatches, electromagnetic clamping devices, and the like. The principlesof the present invention specifically contemplate all such knownclamping alternatives.

After frame 1010 is clamped to platen 1001, as shown at FIG. 11D, avacuum is applied at vacuum orifices 14, which vacuum forms theatmospheric clamping pressure previously disclosed at 20. Onceatmospheric clamping 20 is applied, thermal energy is applied at 22 toraise the temperature of substrate stack 1003 to the desired sublimationtemperature. This atmospheric clamping pressure is maintained onsubstrate stack 1003 for the balance of the imaging process until it isdesirable to remove the several elements of substrate stack 1003following processing. After the desired interval required for dyesublimation imaging, thermal energy is removed at 24 to enable theseveral sheets of substrate 1 to return to their substantially rigidstate. Thereafter, nuts 1022 are removed from bolts 1020, bolts 1020withdrawn from platen 1001 and frame 1010, and frame 1010 removed fromplaten 1001. This enables the removal from platen 1001 of the substratestack 1003 and the separation of that stack into its componentindividual substrates 1 and dye carriers 3. At this point, as before,the image formed by reverse image 5 has been transferred into theseveral ones of the plurality of substrate 1 in substrate stack 103.

This embodiment of the present invention enables significantly longerimaging times. These lengthened imaging times present both advantagesand challenges. One advantage is that a substrate may be imagedthroughout the entire thickness of the substrate, resulting in aparticularly rich, translucent image. The challenge in this case is toconfine the image to one substrate. Long imaging times enable theunwanted migration of dyes from one substrate to another. This can leadnot only to loss of resolution, but loss of registration accuracy, anduneven imaging throughout the several substrates of the substrate stack.

In order to preclude the unwanted migration between substrates, a dyestop may be inserted between individual substrate-dye carrier pairs. Byplacing such a dye stop, for instance a layer of metal foil, between afirst substrate 1 and the dye carrier 3 of the substrate adjacentthereto, this unwanted dye migration may be obviated. The dye stop layermay, with equal facility, be implemented by forming the dye stop as alayer on the side of dye carrier 3 opposite to the image formed thereon,for instance by laminating a layer of metal foil.

While platen assembly 1000, disclosed in FIGS. 11A-F may be utilized inconjunction with any of the previously disclosed apparatuses, theutilization of this platen assembly enables large-scale batch processingof substrate material. One means for implementing such large-scaleproduction utilizes at least one, and preferably a plurality oftransportable platen racks 1200.

Platen rack 1200 in this embodiment takes the form of a movable shelfunit having at least one and preferably a plurality of shelves 1210 forreceiving therein at least one and preferably a plurality of platenassemblies 1000. As it is desirable to maintain atmospheric clampingpressure by means of the vacuum applied to vacuum orifices 14 throughoutthe thermal events of the dye sublimation process taught herein, theseveral vacuum orifices 14 are connected by means of a vacuum hose 1204to a vacuum reservoir 1220 for transportation from an area where platenassemblies 1000 may be loaded to an area where they may be imaged. Suchan area is shown having reference to FIG. 13.

At FIG. 13 is shown an oven 1300 capable of receiving therein at leastone, and preferably a plurality of platen racks 1200. Once the desirednumber of platen assemblies 1000 and platen racks 1200 has been receivedinto an interior portion of oven 1300, oven door 1302 is secured, andthe temperature within oven 1300 elevated to a temperature sufficient toachieve the thermal imaging temperature required by the severalsubstrate elements of substrate stack 1003. This temperature may againbe monitored by means of a thermocouple, inserted beneath membrane 16.

Once the desired imaging temperature has been reached and maintained forthe desired imaging time, the several platen assemblies 1000 may becooled to effect the second thermal event of the dye sublimation imagingprocess taught by the present invention. This cooling may be effected bythe simple expedient of withdrawing platen racks 1200 from oven 1300 andallowing platen racks 1200 and platen assemblies 1000 to cool by naturalair circulation. Alternatively, platen racks 1200, retaining platenassemblies 1000 therein, may be subjected to an active cooling process.Such active cooling may be effected by means of inserting platen racks1200 into a refrigerator, or immersing them in a bath of chilled fluid.Alternatively, where oven 1300 is also equipped with a refrigerationcapability, such refrigeration may be activated and oven 1300 may beutilized to implement an active cooling step.

In one application of this embodiment of the present invention an 80 milAcrylonitrile-Butadiene-Styrene-Copolymer (ABS) sheet was utilized assubstrate 1.

A plurality of ABS sheets were imaged by superposing a dye carrier 3 anda dye stop layer 1003 atop each sheet. The plurality of ABS sheets werethen positioned atop passive cooling device 12. Frame 1010 was thenlowered, covering the several substrate-dye carrier-dye stop stacks withmembrane 16. In this embodiment, a silicone rubber sheet was implementedas membrane 16. After evacuation of the space under membrane 16,processing proceeds in previously discussed for this embodiment. In thiscase the ABS sheets were processed for 3 hours at a temperature of 300°F. After this first thermal event, cooling proceeded as previouslydiscussed.

It should be noted that the use of passive cooling device 12 is optionalin this embodiment.

Yet another embodiment of the present invention is disclosed havingreference to FIGS. 14A-E. This embodiment of the present inventionimplements a vacuum bagging approach to applying the previouslydiscussed vacuum clamping. At FIG. 14A there is shown a vacuum bag orenvelope, 600. Vacuum bag 600 may be advantageously formed from anynumber of heat-resistant, flexible materials which are substantiallyimpervious to air transmission. By way of illustration, but notlimitation, examples of such materials include silicone rubber sheeting,butyl rubber sheeting, heat-resistant plastics and other polymers, andimpregnated fabrics. One material particularly suited for forming vacuumbag 600 of the present invention is a 2 mil advanced nylon sheetingavailable from GEM Polymer Corporation, PO Box 210 Lakeside Avenue,Delano, Pa. 18220-0210. This material is heat-resistant to temperaturesin excess of 400 degrees Fahrenheit and is available either ascustom-made bags, or as rolls of sheet film for user fabrication.

In order to evacuate the interior of vacuum bag 600, a vacuum probe,602, is fitted therethrough. Vacuum probe 602 serves to form avacuum-tight penetration through vacuum bag 600 and to attach a vacuumsource, not shown, for evacuating the interior of vacuum bag 600. Any ofseveral known vacuum probes may be utilized for this function: one suchvacuum probe is a model VP36 available from Torr Technologies, Inc.,1435 22nd St. NW, Auburn, Wash. 98001. Alternative vacuum probes may ofcourse be fitted.

An imaging stack, 640, is made up as follows: a substrate, 1, hassuperposed thereon a dye carrier 3, as previously discussed. Atop dyecarrier 3 is placed a dye stop, 652, consisting of a sheet of aluminumfoil. Alternatively, the side of dye carrier 3 opposite the image sidethereof may have laminated thereon, or printed thereto, a layer of dyestop material, for instance a layer of metalized foil. A plurality ofimaging stacks 640 are further stacked to form imaging body 650.

Imaging body 650 may optionally include one or more accessory layers,654. Examples of these accessory layers include, but are not necessarilylimited to, stiffening plates and pressure leveling layers. By way ofillustration, but not limitation, stiffening plates may be formed ofplywood, metal sheets, and composite materials, including honeycombpanels. Pressure levelers may be implemented utilizing pads ofheat-resistant resilient foam, or other resilient materials. Again, inillustration but not limitation, one example of such heat-resistant foamis a layer of expanded silicone rubber foam.

Once imaging body 650 has been formed, it is inserted into opening 604of vacuum bag 600 as shown at FIG. 14B. Thereafter, as shown at FIG.14C, opening 604 is sealed at 606. Seal 606 may be effected bysubstantially any vacuum sealing methodology known to those havingordinary skill in the art. Again by way of illustration but notlimitation, such seals include the thermal bonding of adjacent portionsof opening 604, the use of sealing extrusions, cements, tapes, glues,clamps, and the closure of opening 604 followed by rolling at least aportion of opening 604 upon itself and thereafter securing that portionwith clamps. Additionally, some of the previously discussed closuremethods may implement the use of sealing compounds, putties or dopes toperfect the previously discussed vacuum seal.

Once seal 606 of vacuum bag 600 has been formed, vacuum bag 600 isevacuated at 620 through vacuum probe 602, forming evacuated imagingpackage 670. A vacuum source, not shown, is utilized to effect thisevacuation. The evacuation of imaging package 670 may utilize vacuumpiping, not shown, which is left in place during the imaging process, ormay utilize a disconnect valve incorporating a vacuum check valve. Thislatter option enables imaging package 670 to be formed and removed fromthe vacuum source during imaging.

Following the formation of imaging package 670, it is heated to performthe previously discussed first thermal event. In one embodiment of thepresent invention, this heating is performed by means of insertingimaging package 670 into an oven, 700, thereafter closing oven doors702, and heating the interior of oven 700 to a desired imagingtemperature. Imaging package 670 is retained within oven 700 for adesired imaging period, and thereafter cooled, to perform the secondthermal event. The cooling of imaging package 670 may be effected aspreviously discussed by means of withdrawing imaging package 670 fromoven 700 and allowing the natural circulation of air to cool imagingpackage 670. Alternatively, imaging package 670 may be cooled by meansof introducing a flow of cooled gas, fluid, or air about imaging package670, or by immersing imaging package 670 into a body of cooled fluid.

Once imaging is completed, vacuum is released from within imagingpackage 670, seal 606 is opened, imaging body 650 removed therefrom, andthe several elements thereof separated resulting in a plurality ofimaged substrates, 1.

In one application of this embodiment of the present invention aplurality of 40 mil polycarbonate sheets, 30 inches by 60 inches, wereimaged by forming imaging body 650 as discussed. Imaging package 670 wasformed by evacuating vacuum bag 600 to a substantially complete vacuum.Thereafter, imaging package 670 was inserted into oven 700 and heated at265° F. for a period of three hours. Following imaging, imaging package670 was removed from oven 700 and allowed to cool utilizing natural aircirculation. Once cooling was effected, vacuum was released and imagingbody 650 separated into its component substrates, as discussed.

Reference was previously made to both those thermal events of a dyesublimation imaging cycle taught by the present invention, and to acontrol station for controlling the several events of such a dyesublimation imaging cycle. Each of these concepts is further exploredhaving reference to FIG. 15. FIG. 15 is a graph of temperature over timeof one dye sublimation imaging cycle utilizing active cooling.

FIG. 15 further includes a time line indicating the several controlactions required to effect the dye sublimation imaging cycle. At time T₁at least one platen is loaded with at least one substrate-dye carrierpair has previously discussed. At this point in time the temperature ofthe substrate-dye carrier pair is the ambient temperature. At time T₂vacuum is applied to the several vacuum orifices 14 of platen assembly204, effecting the previously discussed atmospheric clamping force.Thereafter, at T₃ platen assembly 204 is loaded into the thermal imagingunit of the apparatus. At time T₄ heat is applied through membrane 16 todye carrier 3 and substrate 1. At time T₅ the required dye sublimationtemperature has been attained. The time interval between T₄ and T₅represents the time required to elevate the temperature of substrate 1and dye carrier 3 to the required dye sublimation temperature.Accordingly, it will be appreciated that T₄-T₆ comprises the firstthermal event taught by the present invention. At time T₆ the requireddye sublimation time interval has been achieved, and the time between T₅and T₆ represents this interval. At time T₆ heat is secured, andimmediately thereafter at T₇ cooling is applied to substrate 1 and dyecarrier 3. At time T₈ substrate three has been cooled to itssubstantially rigid temperature and cooling is secured. Accordingly, itwill be appreciated that T₇- T₈ represent the second thermal event ofthe present invention. Thereafter at Tg platen assembly 240 is removedfrom the thermal imaging unit. At time T₁₀ the vacuum is releasedbeneath membrane 16, releasing the atmospheric clamping pressure of thatmembrane to substrate 1 and dye carrier 3. At T₁, the platen 10 may beunloaded and subsequently reloaded for another dye sublimation imagingcycle.

One or more of the control actions indicated may be performed manually,remotely, or automatically. An example of a manual control action iswhere a human operator manually operates a control element, for instanceone of the previously disclosed vacuum, heating, or cooling valves. Aremote control action is where a human operator utilizes a remotecontrol, for instance a switch actuating a remotely controlledelectrical valve, to initiate the control action. An automatic controlaction is where a sequencing device initiates a control action inresponse to a predetermined time interval or to a state indication. Anexample of such a state indication is where the temperature sensed bythermocouple 212 which could not only effect the ramp-up of temperatureshown between T₄ and T₅, and the ramp-down of temperature shown betweenT₇ and T₈, but also could serve to alternately open and close a heatingcontrol valve to maintain the temperature specified between T₅ and T₆.

From the preceding discussion of imaging times, clamping pressures,imaging temperatures, and cooling times, it will be appreciated that theprinciples enumerated herein are applicable over a wide range of thesevariables. While the specifics of any given imaging regime are bothhighly specific and empirically determinable, in general terms, thepresent invention contemplates imaging temperatures for most plasticsubstrates at temperatures between 200° F.-600° F.; more particularlybetween 225° F. and 400° F., and more particularly still at temperaturesbetween 250° F. and 300° F.

Similarly, imaging times of between 15 seconds and 12 hours have beenshown to be advantageous for some embodiments of the present invention.More specifically, imaging times of between 1 minute and 1 may beimplemented with advantage. Still more particularly, imaging timesbetween 3 minutes and 15 minutes have been found satisfactory for someimaging regimes.

In like fashion, imaging pressures equating from 0.25 atmospheres to 20atmospheres may be utilized to advantage. More particularly, suchpressures from 0.5 to 5 atmospheres, and still more particularly,imaging pressures of 0.7 to 1.5 imaging pressures are satisfactory for awide variety of plastic substrates.

From the foregoing discussion of several embodiments of the presentinvention, the ordering or spatial arrangement of the several elementsof these embodiments was presented. It will be appreciated that theseare by way of illustration and not limitation, and the present inventionspecifically contemplates modifications thereto.

Finally, while certain generic and patent plastic substrates have beenpresented as examples herein, the present invention has been found to beutile for imaging a vast array of different plastics. Accordingly, theprinciples of the present invention specifically contemplate theapplication thereof to a wide variety of plastics, and the examplespresented herein are by way of illustration and not limitation.

The present invention has been particularly shown and described withrespect to certain preferred embodiments of features thereof. However,it should be readily apparent to those of ordinary skill in the art thatvarious changes and modifications in form and detail may be made withoutdeparting from the spirit and scope of the invention as set forth in theappended claims. In particular, the principles of the present inventionspecifically contemplate the incorporation of one or more of the variousfeatures and advantages taught herein on a wide variety of dyesublimation apparatuses.

While examples of such alternatives have been presented herewith, itwill be appreciated by those of skill in the art that alternativeorientations of the several elements taught herein, alternative heatingand cooling methodologies, clamping methodologies, and methods forpositioning and indexing platen assemblies may, with equal facility beimplemented to enable the features and advantages taught herein.Similarly, while discussion of the invention disclosed herein hascentered on the utilization of that invention for forming dyesublimation images in solid sheets of plastic, study of the principlesenumerated herein will elucidate to those having skill in the art thatthese principles are applicable to a wide variety of substratesincluding natural and man-made substances, films and polymer-coatedmaterials, including polyesters. Each of these alternatives isspecifically contemplated by the principles of the present invention.

1. Apparatus for forming a dye sublimation image in a substrate with adye carrier having an image formed thereon of a sublimatic dyestuff, theapparatus comprising: a platen, for disposing thereon the substrate, thesubstrate having further disposed thereon the dye carrier such that thesublimatic dyestuff is in contact with the substrate; a membrane forcovering the substrate, the dye carrier, and at least a portion of theplaten; a clamping system for applying, with the membrane, a uniformclamping pressure to the substrate and the dye carrier; a heating devicefor heating the substrate and the dye carrier from their ambienttemperature to a first temperature and for a period of time requisite toform the image in the substrate; and a cooling device for cooling thesubstrate and the dye carrier to a second temperature following theheating thereof.
 2. Apparatus for forming a dye sublimation image in asubstrate utilizing a dye carrier having an image formed thereon of asublimatic dyestuff, the apparatus comprising: a platen, for disposingthereon a substrate, the substrate having further disposed thereon a dyecarrier such that the sublimatic dyestuff is in contact with thesubstrate; a membrane for covering the substrate, the dye carrier, andat least a portion of the platen; an atmospheric clamping system forapplying, in operative combination with the membrane, a uniform clampingpressure to the substrate and the dye carrier; a heating device forheating the substrate and the dye carrier from their ambient temperatureto a first temperature and for a period of time requisite to form theimage in the substrate while the uniform clamping pressure is applied tothe substrate and the dye carrier; and a cooling device for cooling thesubstrate and the dye carrier to a second temperature while the uniformclamping pressure is applied to the substrate and the dye carrier,following the heating thereof.
 3. The apparatus of claim 2 wherein theheating device further comprises a radiant heating element.
 4. Theapparatus of claim 3 wherein the radiant heating element is selectedfrom the group consisting of infrared lamp and microwave source.
 5. Theapparatus of claim 3 wherein the heating device is selected from thegroup consisting of: radiant heating device, conductive heating device,convective heating device, and the application of open flame.
 6. Theapparatus of claim 2 wherein the heating device further comprises aconductive heating device.
 7. The apparatus of claim 6 wherein theconductive heating device further comprises: a thermally conductiveplate; and means for heating the thermally conductive plate.
 8. Theapparatus of claim 6 further comprising a thermally conductive platerendered partially hollow by the formation therein of at least onechamber; a heater for providing a controllable flow of heated fluidthrough the chamber of the thermally conductive plate; and a quantity offluid at least partially filling the chamber of the thermally conductiveplate, and rendered controllably heatable by the heater.
 9. Theapparatus of claim 8 wherein the fluid is selected from the groupconsisting of gas and liquid. 10-42. (canceled)
 43. Apparatus forforming a dye sublimation image in a first surface of a substrate with adye carrier having an image formed thereon of a sublimatic dyestuff, theapparatus comprising: a heater for heating the dye carrier to asublimation temperature; a cooler for cooling the dye carrier; and aclamping pressure system for pressing the image formed on the dyecarrier against the first surface of the substrate, wherein thecontinuous pressure system is able to apply a continuous pressureagainst the first surface of the substrate when the dye carrier issubjected to the heater and when the dye carrier is subjected to thecooler and there between.
 44. The apparatus, as recited in claim 43,wherein the clamping pressure system limits shrinking, enlarging,extruding, and warping of the substrate during the heating and cooling.45. The apparatus, as recited in claim 43, wherein the clamping pressuresystem uses a gas pressure differential to provide the continuouspressure.
 46. The apparatus, as recited in claim 43, wherein theclamping pressure system provides a pressure over an entire surface ofthe dye carrier.
 47. The apparatus, as recited in claim 43, wherein theclamping pressure system provides a pressure of at least 14 pounds persquare inch.
 48. The apparatus, as recited in claim 43, wherein theclamping pressure system limits warping of the substrate during theheating, cooling, and therebetween;
 49. The apparatus, as recited inclaim 43, wherein the clamping pressure system provides an even clampingforce over the entire surface of the substrate.
 50. The apparatus, asrecited in claim 43, wherein the cooler cools the subtrate to atemperature which causes the substrate to be substantially rigid. 51.The apparatus, as recited in claim 43, wherein the heater heats to atemperature of between 200° F.-600° F.
 52. The apparatus, as recited inclaim 43, wherein the clamping pressure system provides a pressure ofbetween 0.25 atmosphers to 20 atmospheres.
 53. The apparatus, as recitedin claim 43, wherein the clamping pressure system is provided by a gaspressure differential to provide the continuous pressure.
 54. Theapparatus, as recited, in claim 43, wherein the heater heats to atemperature and for a period of time requisite to sublimate the imageinto the substrate.